Size-quantized semiconductor nanocrystals possess transient properties from bulk materials to molecules and have been very interesting research subjects. Many researches have been performed using suspended particles in solution. We have investigated preparation methods of nanoparticle films and properties of the prepared films. The following results were obtained in the present study.(1) Immobilization of size-quantized titanium dioxide particles in polyvinylpyrrolidinone (PVPD) gel films was accomplished using electrophoretic deposition of titanium dioxide nanoparticles stabilized by PVPD in 2-propanol. The obtained gel films had high photocatalytic activities for reduction of nitrate ion and carbon dioxide to give ammonia and methanol, respectively. If these films were irradiated in the presence of both nitrate ion and carbon dioxide, urea was photoformed. (2) The films of titanium dioxide nanoparticle immobilized in silica matrices were prepared using the sol-gel technique with hydrolysis of Ti (OEt) _4 and Si (OEt) _4. The photoreduction of carbon dioxide on the prepared films gave carbon monoxide and formate as the reduction products and the ratio of those two kinds of products were influenced by the dielectric constant of the solvents used ; the fraction of formate increased with increase of the dielectric constant of solvent used. (3) The monolayr film of cadmium sulfide nanoparticles was prepared by covalently immobilizing cadimium sulfide nanoparticle to Au (111) with use of chemistry of self-assembling. STM measurements revealed that the obtained monolayr film was composed of the nanoparticles of 2-3 nm diameter without aggregation. Tunneling spectroscopy of a single nanoparticle could be performed, and the energy structure of cadmium sulfide nanoparticle was successfully determined.